1. Field of the Invention
The present invention relates to an encapsulant resin member for a semiconductor, and a semiconductor element encapsulated (sealed) by the use of the resin member and, more particularly, to a solar cell module in which a photovoltaic element is encapsulated by the use of the resin member.
2. Related Background Art
It is conventional practice to encapsulate a semiconductor element such as a photovoltaic element, a photodiode, or the like with a transparent encapsulant resin. For example, a solar cell module is normally constructed in such a structure that a photovoltaic element is encapsulated with an encapsulant resin between a front surface member and a back surface member.
The encapsulant resin is used for the purposes of filling unevenness of the surface of the photovoltaic element and bonding the element to the front surface member and to the back surface member and is usually a transparent, thermoplastic, organic polymer resin. Typical examples are polyvinyl butyral (PVB) and an ethylene-vinyl acetate copolymer (EVA). Among others, EVA is becoming rapidly widespread as an encapsulant resin for the photovoltaic elements, because it is inexpensive, easy to handle, capable of increasing heat resistance by crosslinking, high in durability against long-term outdoor exposure, and so on.
A variety of additives, such as a crosslinking agent, an ultraviolet absorbing agent, an oxidation inhibitor, a silane coupling agent, an adhesive, a reinforcing agent, and so on, are blended in the encapsulant resin in order to enhance the weather resistance, heat resistance, adhesion, impact resistance, etc. of the encapsulant resin. It is ordinary practice to blend these additives in the resin at the stage of producing an encapsulant resin member, for example, a sheet of the encapsulant resin, and they exist uniformly in the direction of thickness of the sheet.
The photovoltaic element is placed via this sheet of an encapsulant resin between the front surface member and the back surface member to form a solar cell module stack and the solar cell module stack is thermally compressed while being deaerated, to be laminated, thereby obtaining a solar cell module.
However, the inventors have found out that, because in the conventional process the concentrations of the additives in the encapsulant resin member were uniform in the direction of thickness of the encapsulant resin member, the additives more than necessary had to be blended in order to perform the aimed functions effectively. These excess additives are apt to be evaporated or decomposed readily by heat during the laminating operation of the photovoltaic element with the encapsulant resin member, so as to remain in the form of bubbles in the surface of the module. These remaining bubbles will degrade the appearance and will be the cause of decreasing the yield of the solar cell module. Further, hitherto, when the adhesion between the photovoltaic element and the encapsulant resin member was to be improved, it was conventional practice to directly coat the bonding surfaces with a silane coupling agent before the laminating operation with the encapsulant resin. Alternatively, when the front surface member such as glass sheet was bonded to the encapsulant resin member, it was conventional practice to directly coat the glass surface with a silane coupling agent before the laminating operation with the encapsulant resin.
For solving the above issue, the present invention provides an encapsulant resin member for a semiconductor having an additive dissolved therein such that the concentration of the additive has a gradient in the direction of thickness of the encapsulant resin member.
The present invention also provides a method of producing a semiconductor, comprising stacking on a surface of a semiconductor element at least two types of organic polymer resin members having different contents of an additive dissolved therein and encapsulating the semiconductor with the resin.
The present invention also provides a method of producing a semiconductor, comprising applying an electric field to an encapsulant resin member to effect electrophoresis of a polar additive dissolved in the encapsulant resin thereby establishing a concentration gradient of the additive in the direction of thickness of the encapsulant resin member and encapsulating a surface of a semiconductor with the encapsulant resin.
The present invention also provides a method of producing a solar cell module, comprising stacking on a surface of a photovoltaic element at least two types of organic polymer resin members having different contents of an additive dissolved therein and encapsulating the photovoltaic element with the resin.
The present invention also provides a method of producing a solar cell module, comprising applying an electric field to an encapsulant resin member to effect electrophoresis of a polar additive dissolved in the encapsulant resin thereby establishing a concentration gradient of the additive in the direction of thickness of the encapsulant resin member and encapsulating a surface of a photovoltaic element with the encapsulant resin.
The present invention also provides a semiconductor element encapsulated with an encapsulant resin, wherein an additive dissolved in the encapsulant resin has a concentration gradient in the direction of thickness of the encapsulant resin.
The present invention also provides a method of producing a semiconductor element encapsulated with an encapsulant resin, comprising providing an additive dissolved in the encapsulant resin with a concentration gradient in the direction of thickness of the encapsulant resin.
The following methods can be included as methods for establishing the concentration gradient of the additive in the direction of thickness of the encapsulant resin member. One method is a method of stacking at least two types of organic polymer resin members such as organic polymer resin sheets containing different contents of the additive, on a surface of a semiconductor element and encapsulating the semiconductor with the resin.
Another method is a method of applying an electric field to an encapsulant resin member to effect electrophoresis of a polar additive in the encapsulant resin member, so as to establish a concentration gradient of the additive in the direction of thickness of the encapsulant resin member and encapsulating a surface of a semiconductor with the resin. The method of applying the electric field to the surface of the encapsulant resin herein can be either a method of applying the electric field from the outside in forced fashion or a method of placing on the encapsulant resin member a charged organic polymer resin member, for example, an organic polymer resin layer having a surface subjected to the corona discharge or plasma discharge treatment to apply the electric field.
As the additive in the encapsulant resin, a polar substance is used when expected to have the concentration gradient, while a nonpolar substance is used when expected to have a uniform concentration distribution.
The encapsulant resin member of the present invention has the additive dissolved therein such that the additive has the concentration gradient in the direction of thickness and is therefore a highly functional encapsulant resin member for a semiconductor. For example, in the case of the solar cell module, when the additive such as an ultraviolet absorbing agent or the like in the encapsulant resin is made to exist in a higher concentration in the vicinity of the surface on the light-incidence side of the encapsulant resin member, whereby deterioration of the encapsulant resin and the photovoltaic element below the encapsulant resin due to ultraviolet rays can be prevented efficiently even if the amount of the additive is relatively small.
The additive like the silane coupling agent in the encapsulant resin member can enhance the adhesive force between the encapsulant resin and the front surface member or between the encapsulant resin and the photovoltaic element when existing in a high concentration in the vicinity of the front surface member or the photovoltaic element. Especially, in the present invention, it is preferred that the concentration of the silane coupling agent in the encapsulant resin member is higher at a location near the front surface member but lower at a location remote from the front surface member, so as to improve the adhesion between the front surface member such as glass sheet and the encapsulant resin member.
Thus, by establishing the concentration gradient of the additive dissolved in the encapsulant resin in the direction of thickness thereof as described above, the aimed function can be achieved by a minimum amount of the additive. It can also eliminate the negative effect that the excess additive is evaporated or decomposed during the laminating operation to remain in the form of bubbles in the module surface. Since the concentration gradient can be established selectively, it also becomes possible to prevent antagonistic action between additives, for example, between a crosslinking agent and an oxidation inhibitor, which is such interaction between the additives as to degrade abilities thereof, and, conversely, to promote synergistic effect, for example, occurring between an ultraviolet absorbing agent and a light stabilizer, which is such interaction as to enhance abilities thereof.